1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording for use to write data on a recording medium by means of a perpendicular magnetic recording system.
2. Description of the Related Art
The recording systems of magnetic read/write apparatuses include a longitudinal magnetic recording system in which the magnetization of signals is directed along the plane of a recording medium (the longitudinal direction), and a perpendicular magnetic recording system in which the magnetization of signals is directed perpendicular to the plane of a recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density, compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, like those for longitudinal magnetic recording, a structure in which a read head unit including a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head unit including an induction-type electromagnetic transducer for writing are stacked on a substrate. The write head unit includes a coil and a main pole. The main pole has an end face located in a medium facing surface configured to face a recording medium. The coil produces a magnetic field corresponding to data to be written on the recording medium. The main pole passes a magnetic flux corresponding to the magnetic field produced by the coil, and produces a write magnetic field from its end face.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end). An airflow that comes from the air inflow end into the space between the medium facing surface and the recording medium causes the slider to slightly fly over the surface of the recording medium.
Here, the side of the positions closer to the leading end relative to a reference position will be referred to as the leading side, and the side of the positions closer to the trailing end relative to the reference position will be referred to as the trailing side. The leading side is the rear side in the direction of travel of the recording medium relative to the slider. The trailing side is the front side in the direction of travel of the recording medium relative to the slider.
The magnetic head is typically disposed near the trailing end of the medium facing surface of the slider. In a magnetic disk drive, positioning of the magnetic head is performed by a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs depending on the position of the magnetic head across the tracks.
Particularly, in a magnetic disk drive of the perpendicular magnetic recording system which is higher in capability of writing on a recording medium than the longitudinal magnetic recording system, the skew mentioned above can cause the phenomenon that signals already written on one or more tracks that are adjacent to a track targeted for writing are erased or attenuated during writing of a signal on the track targeted for writing. In the present application, this phenomenon will be called unwanted erasure. The unwanted erasure includes adjacent track erasure (ATE) and wide-area track erasure (WATE). To achieve higher recording densities, it is necessary to prevent the occurrence of unwanted erasure.
In order to prevent the occurrence of unwanted erasure induced by a skew and achieve higher recording densities, it is effective to configure the main pole so that the thickness of its portion near the medium facing surface decreases with increasing proximity to the medium facing surface, and also provide a write shield that has an end face located in the medium facing surface and surrounding the end face of the main pole.
In a magnetic head including the write shield, there is typically provided a return path section for connecting the write shield to a portion of the main pole located away from the medium facing surface. The write shield, the return path section and the main pole define a space for a portion of the coil to pass therethrough. The write shield and the return path section have the function of capturing a magnetic flux that is produced from the end face of the main pole and spreads in directions other than a direction perpendicular to the plane of the recording medium, thereby preventing the magnetic flux from reaching the recording medium. The write shield and the return path section further have the function of allowing a magnetic flux that has been produced from the end face of the main pole and has magnetized a portion of the recording medium to flow back to the main pole.
With increases in frequency of write signals to achieve higher recording densities, it is required of the magnetic head that the write current flowing through the coil should exhibit a rapid rise. To meet such a requirement, it is effective to reduce the length of a magnetic path that passes through the write shield, the return path section and the main pole. To achieve this, it is effective to reduce the distance between the medium facing surface and an end of the coil that is closest to the medium facing surface.
A magnetic head in which the write shield includes a leading shield and a trailing shield is known to be suitable to prevent the occurrence of unwanted erasure induced by a skew. Such a magnetic head includes a leading-side return path section connected to the leading shield, and a trailing-side return path section connected to the trailing shield. The leading-side return path section and the main pole define a first space therebetween. The trailing-side return path section and the main pole define a second space therebetween. The coil includes at least one first coil element passing through the first space, and at least one second coil element passing through the second space. The magnetic head of such a structure is disclosed in, for example, U.S. Pat. No. 8,810,963 B1 and US 2016/0275970 A1.
In order for the magnetic head of the foregoing structure to achieve higher recording density while minimizing leakage of magnetic flux from some midpoint in the main pole, it is effective to provide the the main pole with a bottom end including an inclined portion, as disclosed in U.S. Pat. No. 8,810,963 B1 and US 2016/0275970 A1. The inclined portion has a first end located in the medium facing surface and a second end opposite thereto. The inclined portion is inclined with respect to the medium facing surface and a direction perpendicular to the medium facing surface such that the second end is located on the leading side relative to the first end.
However, there are the following first and second problems with the structure disclosed in U.S. Pat. No. 8,810,963 B1 and US 2016/0275970 A1. The first problem is leakage of magnetic flux from the main pole to the leading-side return path section. The second problem is that a magnetic path passing through the leading shield, the leading-side return path section and the main pole is longer than a magnetic path passing through the trailing shield, the trailing-side return path section and the main pole.